Pattern inspection method and pattern inspection system

ABSTRACT

A pattern data examination method and system capable of accurately and speedily examining a circuit pattern without failing to extract pattern contour data are provided. While pattern comparison is ordinarily made by using a secondary electron image, a contour of a pattern element is extracted by using a backscattered electron image said to be suitable for observation and examination of a three dimensional configuration of a pattern element, and pattern inspection is executed by using the extracted contour of the pattern element. More specifically, pattern inspection is executed by comparing a contour of a pattern element with design data such as CAD data to measure a difference between the contour and the data, and by computing, for example, the size of the circuit pattern element from the contour of a pattern. From two or more backscattered electron images formed by detecting backscattered electrons at two or more different spatial positions, pattern contour data contained in the backscattered electron images may be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/188,096 filed Aug. 7, 2008 and claims priority of Japanese patentapplication no. 2007-209789 filed Aug. 10, 2007, the disclosures ofwhich are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern inspection method and apattern inspection system and, more particularly, to a patterninspection method and a pattern inspection system for examining apattern formed on a substrate by using a photographic image of asemiconductor circuit and design data of the semiconductor circuit.

2. Background Art

In recent years, the development of semiconductor devices manufacturedby finer patterning, having increased numbers of layers in multiplayerstructure and complicated in logic has been pursued. In the presentcircumstances, it is extremely difficult to manufacture suchsemiconductor devices. As a result, the occurrence of defects comingfrom manufacturing processes tends to increase, and it is important toefficiently and correctly detect such defects and to identifymanufacturing process problems.

The kinds of possible defects from a manufacturing process includedeformation, breakage and short circuit of a pattern. Such defects canbe detected by comparison with a reference pattern having an idealshape. More specifically, an operator selects a pattern element havingan ideal shape from patterns formed on a wafer. An image of the patternelement is taken (as a reference pattern). Subsequently, an image of apattern to be examined is taken; the positions of the image of theobject to be examined and the reference pattern element are adjusted;and a difference therebetween is computed. If the pattern to be examinedincludes a defect, luminance information at a position corresponding tothe defect differs from luminance information about the referencepattern element and, correspondingly, the amount of difference isincreased. By utilizing this nature, a position at which a differentialvalue equal to or larger than a certain value is exhibited is detectedas a defect position.

Such inspection is carried out with a review scanning electronmicroscope (review SEM) such as one disclosed in JP Patent ApplicationNo. 11-343094 (1999). The review SEM irradiates a specimen with anelectron beam and performs the above-described inspection by using animage formed by using secondary electrons and backscattered electronsemitted from the specimen surface. An ordinary review SEM has asecondary electron detector for detecting secondary electrons and abackscattered electron detector for detecting backscattered electrons.Signals from the respective detectors are formed as a secondary electronimage and a backscattered electron image. Each of the electron images isseen in different ways due to the difference between the characteristicsof electrons used to form the images. The secondary electron image issuitable for observation and inspection of a pattern configuration,while the backscattered electron image is suitable for observation andinspection of a three-dimensional configuration of a pattern. However,the backscattered electron detector cannot detect backscatteredelectrons from a portion of the pattern element shielded with the majorportion of the pattern element as seen from the position at which thebackscattered electron detector is disposed. Therefore, threedimensional configuration of the whole pattern element cannot beexpressed from a backscattered electron image formed by onebackscattered electron detector. To enable observation of details of athree-dimensional configuration of a pattern, therefore, backscatteredelectron detectors are disposed at very small intervals so as tosurround a specimen, and a plurality of backscattered electron imagesemitted from the pattern are formed. In an ordinary review SEM, however,two or three backscattered electron detectors are provided byconsidering the equipment cost and the installation area and aredisposed so as to surround a specimen to obtain a plurality ofbackscattered electron images. Images used for pattern inspection areselectively used according to inspection purposes in such a manner thatordinary pattern inspection is performed by inspection through secondaryelectron images while inspection of a three-dimensional configuration ofa pattern or a defect is performed by using backscattered electronimages.

In a case where a pattern with openings such as holes is inspected,emission of secondary electrons from a hole area is weak. In such acase, an inspection method such as disclosed in JP Patent Publication(Kokai) No. 2000-260380 is used in which a backscattered electron imageis blended at a certain ratio with a secondary electron image in animage of a hole area.

A mode of inspection using a reference pattern taken as an image asdisclosed in JP Patent Application No. 11-343094 (1999) and JP PatentPublication (Kokai) 2000-260380 requires a user operation to registerthe reference pattern and, therefore, entails a problem in that aconsiderably long time is required for the reference pattern registeringoperation if patterns of various configurations are inspected.

Trials have therefore been made to automate the reference patternregistering operation and reduce the inspection time by adopting amethod of using design data for a semiconductor device for a referencepattern and detecting a defect by comparing the design data and apattern. For example, JP Patent Publication (Kokai) No. 2005-277395discloses detection of a defect through comparison between design dataand a pattern. More specifically, a manufactured semiconductor structureis irradiated with an electron beam; a contour line in a pattern isextracted by image processing from a secondary electron image formed bydetecting secondary electrons emitted from the surface of thesemiconductor structure; the contour line and the corresponding shapeaccording to design data is compared with each other; and a portion ofthe pattern having a difference in shape is detected as a defect.

SUMMARY OF THE INVENTION

However, there is a possibility of the contrast of the secondaryelectron image varying largely under the influence of electrificationcaused on the semiconductor surface by irradiation with the electronbeam. Therefore, even the method disclosed in JP Patent Publication(Kokai) No. 2005-277395 entails difficulty in extraction of a patterncontour line by image processing and, hence, difficulty in comparingdesign data and the contour line.

On the other hand, backscattered electron images used in a review SEM orthe like has such a characteristic as to be unsusceptible toelectrification in comparison with secondary electron images. Withbackscattered electron images, however, there is a problem that theshape of a portion of pattern element shielded with the major portion ofthe pattern element cannot be expressed because of the characteristicsof backscattered electrons, as described above. Presently, therefore,backscattered electron images are not used as an image for comparisonwith design data.

The present invention has been achieved in view of these circumstances,and an object of the present invention is to provide a pattern dataexamination method and system capable of accurately and speedilyexamining a circuit pattern without failing to extract pattern contourdata.

-   (1) To achieve the above-described object, a contour of a pattern    element is extracted by using a backscattered electron image said to    be suitable for observation and inspection of a three-dimensional    configuration of a pattern, while pattern comparison is ordinarily    made by using a secondary electron image. Pattern inspection is    executed by using the extracted contour of the pattern element. More    specifically, pattern inspection is executed by comparing a contour    of a pattern element with design data such as CAD data to measure a    difference between the contour and the data, and by computing, for    example, the size of the circuit pattern element from the contour of    a pattern.-   (2) That is, a pattern inspection method in accordance with the    present invention is a method in which a circuit pattern on a    specimen manufactured on the basis of design data for an electronic    device is examined by comparison between the design data and an    image of the circuit pattern, and which is characterized by    including a step in which the specimen is irradiated with an    electron beam, backscattered electrons emitted from the specimen are    detected by a backscattered electron detector, and backscattered    electron image forming means forms a backscattered electron image by    using the detected backscattered electrons, and a step in which    contour extraction means extracts contour data on a contour in the    circuit pattern from the backscattered electron image formed. This    method is implemented, for example, as software. In such a case, the    above-described backscattered electron image forming means and    contour extraction means are implemented by means of a computer such    as a processing control section or a CPU according to a program.

In the present invention, two or more backscattered electron detectorsmay be disposed to detect backscattered electrons at different spatialpositions and form two or more backscattered electron images. In such acase, circuit pattern contour data is extracted from a combined imageobtained by combining the two or more backscattered electron images. Toextract the contour data, inter-image computational processing on thetwo or more backscattered electron images is executed. As theinter-image computational processing, any one of the following threesteps is executed. 1) first computational processing for comparing thetwo or more backscattered electron images and selecting thebackscattered electron image having a higher gray-level value as thecombined image of the backscattered electrons, 2) second computationalprocessing for comparing the two or more backscattered electron imagesand selecting the backscattered electron image having a lower gray-levelvalue as the combined image of the backscattered electrons, and 3) thirdcomputational processing for generating a gray-level value of thecombined image of the backscattered electrons by adding together thegray-level values of the two or more backscattered electron images ineven or uneven proportions.

-   (3) A pattern inspection method according to another aspect of the    present invention is a method in which a circuit pattern on a    specimen manufactured on the basis of design data for an electronic    device is examined by comparison between the design data and an    image of the circuit pattern, and which is characterized by    including a step in which the specimen is irradiated with an    electron beam, backscattered electrons emitted from the specimen are    detected by a backscattered electron detector, and backscattered    electron image forming means forms a backscattered electron image by    using the detected backscattered electrons, a step in which    secondary electrons emitted from the specimen are detected by a    secondary electron detector, and secondary electron image forming    means forms a secondary electron image by using the detected    secondary electrons, and a step in which contour extraction means    extracts contour data on a contour in the circuit pattern from the    backscattered electron image and the secondary electron image.

Also in this aspect, two or more backscattered electron detectors may bedisposed to detect backscattered electrons at different spatialpositions and form two or more backscattered electron images. In such acase, the contour extraction means forms a combined image from two ormore backscattered electron images and a secondary electron image byusing inter-image computational processing and extracts circuit patterncontour data from the combined image. As the inter-image computationalprocessing, any one of the following three steps is executed. 1) firstcomputational processing for comparing the two or more backscatteredelectron images and the secondary electron image and selecting thebackscattered electron image having a higher gray-level value or thesecondary electron image as the combined image of the backscatteredelectrons, 2) second computational processing for comparing the two ormore backscattered electron images and the secondary electron image andselecting the backscattered electron image having a lower gray-levelvalue or the secondary image as the combined image of the backscatteredelectrons, and 3) third computational processing for generating agray-level value of the combined image of the backscattered electrons byadding together the gray-level values of the two or more backscatteredelectron images and the secondary electron image in even or unevenproportions.

-   (4) Pattern inspection is executed by comparing the extracted    contour data and the design data. For example, a difference between    the contour data and the pattern according to the design data is    measured; a portion of the pattern is detected as a defective    portion if the portion has as the measured value a value larger than    a prescribed value; and a circuit pattern size of a circuit pattern    spacing size on the specimen is computed from the contour data.-   (5) The backscattered electron image, the contour data and the    design data may be displayed in a state of being overlaid on each    other or arranged side by side on a screen of a display unit.-   (6) The specimen is a mask or a silicon wafer. The two or more    backscattered electron detectors are disposed at substantially equal    intervals so as to surround the specimen. For example, three    backscattered electron detectors are provided and disposed at    intervals of about 120 degrees from each other.

Also, the inter-image computational processing may include smoothing ofthe combined image, whereby noise superimposed on the combined image isreduced and luminance-changed portions of the pattern in the combinedimage are reduced.

-   (7) The present invention provides a pattern inspection system    corresponding to the above-described pattern inspection method.    Other features of the present invention will become apparent from    the best mode of carrying out the invention described below with    reference to the accompanying drawings.

According to the present invention, contour data for a pattern isextracted from backscattered electron images unsusceptible toelectrification and the pattern is examined by comparison with thedesign data. As a result, an increase in semiconductor circuitobservation time due to measures against electrification and failure toextract contour data due to an image disturbance caused byelectrification can be avoided, and semiconductor device examination canbe performed speedily and accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the configuration of a patterninspection system in accordance with the present invention.

FIGS. 2A and 2B are diagrams showing a procedure for forming a secondaryelectron image and a backscattered electron image.

FIG. 3 is a flowchart showing a pattern inspection procedure in thepattern inspection system in accordance with the present invention.

FIG. 4 is a diagram showing an example of an automatic focusing point,an astigmatism point and other points on a design layout required fortaking an image at an examination point on a semiconductor wafer.

FIG. 5 is a flowchart for explaining pattern inspection processingaccording to the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of disposition of backscatteredelectron detectors.

FIGS. 7A to 7C are diagrams showing backscattered electron images.

FIGS. 8A and 8B are diagrams showing methods 1 and 2 of forming acontour line from an image.

FIG. 9 is a diagram showing backscattered electron images.

FIGS. 10A to 10C are diagrams showing combined backscattered electronimages.

FIG. 11 is a diagram showing an example of combining of backscatteredelectron images.

FIG. 12 is a diagram showing an example of combining of backscatteredelectron images.

FIG. 13 is a diagram showing an example of disposition of backscatteredelectron detectors about a specimen.

FIG. 14 is a flowchart showing details of contour line extractionprocessing (S504).

FIG. 15 is a diagram showing contour data extracted from a combinedbackscattered electron image.

FIG. 16 is a flowchart showing details of comparison examinationprocessing using design data and contour data (S505).

FIGS. 17A and 17B are diagrams showing a positional relationship betweendesign data and contour data when a view field misalignment exists and apositional relationship between design data and contour data in a casewhere position correction is made by pattern matching.

FIGS. 18A to 18C are diagrams showing an example of shape comparisonbetween design data and contour data.

FIG. 19 is a diagram showing an on-screen display for informing a userof the state of pattern inspection and examination results.

FIG. 20 is a flowchart in a case where only size measurement isperformed.

FIG. 21 is a flowchart for explaining pattern inspection processingaccording to a second embodiment of the present invention.

FIGS. 22A to 22E are diagrams showing the difference between a combinedbackscattered electron image and a secondary electron image.

FIG. 23 is a diagram showing table data for changing images from whichcontour lines are extracted, according to semiconductor wafer imagetaking conditions and wafer conditions.

DESCRIPTION OF SYMBOLS

-   100 Pattern inspection system-   101 Semiconductor wafer-   102 Electronic optical system-   103 Electron gun-   104 Primary electrons-   105 Condenser lens-   106 Deflector-   107 ExB deflector-   108 Objective lens-   109 Secondary electron detector-   110, 111 Backscattered electron detector-   112, 113, 114 A/D converter-   115 Processing control section-   151 CPU-   152 Image memory-   153 LSI-   116 Computer-   117 Stage-   119 Stage controller-   120 Deflection control section-   121 Focus control section-   123 Storage-   125 Image taking recipe preparation section-   130 Design system-   201, 202, 203 Scanning with electron beam in x-direction-   204, 205, 206 Scanning with electron beam in y-direction-   401 Design layout-   402 Focusing point-   403 Addressing point-   404 Brightness/contrast point-   405 Examination point-   406 Automatic astigmatism correction point-   601 Backscattered electron detector (L)-   602 Backscattered electron detector (R)-   701 Pattern portion expressed as white line-   702 Pattern portion expressed by stepped-luminance-change portion-   1701 Contour data-   1702 Design data-   1801 Straight line constituting contour data-   1802 Straight line constituting design data-   1803 Distance between design data and contour line data-   1804 Pattern cut portion-   1805 Pattern short circuit portion-   1901 Display screen-   1902 BSE image display view-   1903 Combined BSE image display view-   1904 Examination state display view-   1905 Examination result display view-   1906 On-wafer examination point display view-   2201 Contour line extraction failure portion

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings. It is to be noted that the embodimentsdescribed below are only examples of implementation of the presentinvention, and that the embodiments do not limit the technical scope ofthe invention. Constituent elements common to the drawings are indicatedby the same reference numerals.

<First Embodiment>

(1) Configuration of a Pattern Inspection System Using SEM

FIG. 1 is a diagram schematically showing the configuration of a patterninspection system 1 in accordance with the present invention. Thepattern inspection system 100 is provided with a scanning electronmicroscope (SEM) capable of obtaining a backscattered electron (BSE)image and a secondary electron (SE) image of a semiconductor pattern. Anelectron optical system 102 of the SEM has an electron gun 103 whichproduces an electron beam (primary electrons) 104, a condenser lens 105which converges the electron beam 104 generated from the electron gun103, a deflector 106 which deflects the converged electron beam 104, anExB deflector 107 for detecting secondary electrons, and an objectivelens 108 which focuses the converged electron beam on a semiconductorwafer 101. The semiconductor wafer 101 is placed on an XY stage 117.With the deflector 106 and the objective lens 108, the electron beamapplication position and the aperture are controlled so that theelectron beam is applied and focused to a desired point on thesemiconductor wafer 101 placed on the XY stage 117. With the XY stage117, the semiconductor wafer 101 is moved to enable taking an image ofthe semiconductor wafer 101 at desired position. Accordingly, changingthe observation position by means of the XY stage 117 is referred to asstage shifting, while changing the observation position by deflectingthe electron beam by means of the deflector 106 is referred to as beamshifting.

From the semiconductor wafer 101 to which the electron beam is applied,secondary electrons and backscattered electrons are emitted. Thesecondary electrons are detected by a secondary electron detector 109.The backscattered electrons are detected by backscattered electrondetectors 110 and 111. The backscattered electron detectors 110 and 111are disposed at positions different from each other. The secondaryelectrons and backscattered electrons detected by the secondary electrondetector 109 and the backscattered electron detectors 110 and 111 areconverted into digital signals by A/D converters 112, 113, and 114 to beinput to a processing control section 115 and stored in an image memory152. Image processing is performed on the stored secondary electrons andbackscattered electrons by means of components such as a centralprocessing unit (CPU) 151 and image processing hardware 153 according toa purpose, thereby examining a semiconductor pattern. That is, theprocessing control section 115 sends control signals to a stagecontroller 119 and a deflection control section 120 to take images at anaddressing point (AP), a focusing point (FP), an astigmatism point (SP),a brightness/contrast point (BP) and an examination point (EP) describedbelow on the basis of an image taking recipe prepared in an image takingrecipe preparation section 125 described below, and showing a patterninspection procedure, and examines the semiconductor pattern byperforming processing and control including various kinds of imageprocessing and the like on the observed image on the semiconductor wafer101.

The processing control section 115 is connected to the stage controller119, the deflection control section 120 and a focus control section 121.The stage controller 119 performs control of the position and movementof the stage 117 including global alignment control for correcting anorigin misalignment and rotation of the semiconductor wafer 101 byobserving global alignment marks on the semiconductor wafer 101 throughan optical microscope (not shown) or the like. The deflection controlsection 120 controls beam shifting of the electron beam (beamdeflection) by controlling the deflector 106. The focus control section121 performs focus control by controlling the objective lens 108.

The processing control section 115 is also connected to a computer(including a display) 116 having input means to have the functions of agraphical user interface (GUI) or the like for displaying images,examination results, etc., to a user. While an example of the systemhaving two backscattered electron image detectors has been described,the number of backscattered electron image detectors can be increased.Also, processing and control in the processing control section 115 canbe performed by assigning part or the whole of control in the processingcontrol section 115 to the computer 116 or the like incorporating a CPUand a memory capable of storing images.

Further, the processing control section 115 is connected via a network,a bus or the like to the image taking recipe preparation section 125that prepares an image taking recipe including information such as thecoordinates of one of or a plurality (or all) of the below-described AP,FP, SP, BP and EP, a design data template for positioning correspondingto the coordinates, and SEM observation conditions (including the imagetaking magnification and image quality). The image taking recipepreparation section 125 is connected via a network or the like to adesign system 130 such as an electronic design automation (EDA) tool toobtain design data. The image taking recipe preparation section 125prepares an image taking recipe from information on image taking pointsof the semiconductor wafer to be examined, by using design data. Theimage taking recipe preparation section 125 corresponds to an imagetaking recipe preparation apparatus disclosed in JP Patent Publication(Kokai) No. 2006-351746 for example. However, the concept of preparationof an image taking recipe from design data itself has been proposed fora long time. The method and apparatus for producing an image takingrecipe from design data are not restrictively specified in the presentinvention. In ordinary cases, preparation of an image taking recipe isexecuted by means of software processing in an electronic computerincluding a CPU and a memory or hardware processing using hardwareincluding a CPU, an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) and a memory.

(2) About Visualization of Detected Electrons

FIG. 2 is a diagram for explaining a method of visualizing the amountsof signals obtained from electrons emitted from the surface of thesemiconductor wafer when the surface of the semiconductor wafer isirradiated and scanned with the electron beam. Application of theelectron beam for irradiation and scanning is performed in the x- ory-direction, for example, as indicated by lines 201 to 203 or lines 204to 206 in FIG. 2A. The direction of scanning can be changed by changingthe direction of deflection of the electron beam.

In FIG. 2A, G1 to G3 respectively indicate points on semiconductor waferto which electron beams 201 to 203 in scanning in the x-direction areapplied. Similarly, G4 to G6 respectively indicate points onsemiconductor wafer to which electron beams 204 to 206 in scanning inthe y-direction are applied. The amounts of signals obtained fromsecondary electrons emitted in G1 to G6 are converted into brightnessvalues of pixels H1 to H6 in the image coordinate system shown in FIG.2B through the secondary electron detector and the AD converter, whilethe amounts of signals obtained from backscattered electrons emitted inG1 to G6 are converted into brightness values of pixels H1 to H6 throughthe backscattered electron detectors and the AD converter (subscriptsafter G and H corresponding to each other). An SE image is formed fromthe amounts of signals obtained from the secondary electrons, while aBSE image is formed from the amounts of signals obtained from thebackscattered electrons.

(3) About Image Taking Sequence

FIG. 3 is a diagram for explaining an image taking sequence forobservation of an arbitrary EP on the wafer. FIG. 4 is a diagram showingan example of setting AP 403, FP 402, SP 406 and BP 404 with respect toEP 405 on a design layout. Image taking positions and image takingconditions (including the image taking magnification and image quality)in the image taking sequence and examination conditions at the EP areprepared as an image taking recipe in the image taking recipepreparation section 225 on the basis of design data and examinationpoint information and are managed by being stored in a storage 123 forexample.

Referring to FIG. 3, the semiconductor wafer 101 is first mounted on thestage 117 (S301). Subsequently, an origin misalignment and a rotationalmisalignment of the specimen are computed by the processing controlsection 115 on the basis of the results of observation of globalalignment marks on the specimen through an optical microscope or thelike (not shown) and the misalignments are corrected by controlling thestage 117 on the basis of the amounts of these misalignments by means ofthe stage controller 119 (S302).

Next, the processing control section 115 controls the stage 117 to movethe image taking position to the AP according to the coordinates of theimage taking points and image taking conditions prepared by the imagetaking recipe preparation section 125, and performs image taking at animage taking magnification lower than that at the time of EP imagetaking (S303). Description about the AP is made below. Directobservation of the EP entails a problem in that a portion to be observedmay deviate from the field of view of the SEM due to the stagepositioning accuracy for example. To solve this problem, the processingcontrol section 115 temporarily observes the AP that has been preparedin advance in the image taking recipe preparation section 125 forpositioning and registered in the storage 123 and whose coordinates areknown, and performs matching between the design data template at the APprepared in advance by the image taking recipe preparation section 125and registered in the storage 123 and the SEM image at the AP observed.A shift vector between the center coordinates of the design datatemplate and the center coordinates at the time of actual observation atthe AP is thereby detected. Subsequently, the processing control section115 shifts the beam (changes the application position by inclining thebeam incidence direction) by an amount corresponding to the result ofsubtraction of the detected shift vector from the relative vectorbetween the coordinates of the design data template and the coordinatesof the EP by controlling the deflector 106 through the deflectioncontrol section 120. The processing control section 115 thereby movesthe image taking position and observes the EP, thus enabling imagetaking at the EP with high coordinate accuracy. (The beam shiftpositioning accuracy is ordinarily higher than the stage positioningaccuracy.)

The image taking position is moved to the FP by beam shifting on thebasis of control and processing performed by the processing controlsection 115 and images are taken to obtain automatic focusingparameters, and automatic focusing is performed on the basis of theobtained parameters (S304).

Subsequently, the image taking position is moved to the SP by beamshifting on the basis of control and processing performed by theprocessing control section 115 and images are taken to obtainastigmatism correction parameters, and automatic astigmatism correction(automatic stigmatism correction) is performed on the basis of theobtained parameters (S305).

Further, the image taking position is moved to the BP by beam shiftingon the basis of control and processing performed by the processingcontrol section 115 and images are taken to obtain brightness/contrastadjustment parameters, and automatic brightness/contrast adjustment isperformed on the basis of the obtained parameters (S306). Part or all ofaddressing, automatic focusing, automatic astigmatism correction andautomatic brightness/contrast adjustment in the above-described stepsS303, S304, 5305 and S306 are omitted in some case. The order of thesteps S303, S304, S305 and S306 may alternatively be changed asrequired. Other variations of these operations are conceivable. Forexample, some of the coordinates of the AP, FP, SP and BP may coincidewith each other (for example, automatic focusing and automaticastigmatism correction are performed at the same position).

Finally, the image taking position is moved to the EP by beam shiftingon the basis of control and processing performed by the processingcontrol section 115, and images are taken to examine the pattern (S307).

(4) About Pattern Inspection Processing

FIG. 5 is a flowchart for explaining pattern inspection processing inaccordance with the present invention. This pattern inspectionprocessing is executed by means of software processing using the CPU151, the image memory 152 and the like of the processing control section115. However, this pattern inspection processing may alternatively beexecuted by means of software processing using a CPU, a memory and othercomponents of an electronic computer to which images from the SEMapparatus and the design data template from the image taking recipepreparation section 125 can be input via a LAN and a bus or a storagemedium such as a portable memory device or a hard disk. Detaileddescription will be made of each block below.

Referring to FIG. 5, the processing control section 115 (CPU 151) firstreads the design data template corresponding to the coordinates of theEP from the image taking recipe preparation system 125 (S501).Subsequently, the processing control section 115 (CPU 151) reads fromthe image memory 152 a plurality of BSE images at the EP taken from aplurality of viewing points (S502) and forms a combined BSE image bycombining processing (S503). The processing control section 115 (CPU151) extracts a contour line from the combined BSE image (S504) andexamines the pattern by comparing the contour data and the design data(S505). Data (configuration information including the coordinateposition and length) on a defect in the pattern detected by comparingthe pattern configuration according to the design data and the patternconfiguration according to the contour data as described above iswritten to the storage 123 for example (S506). Details of the processingfrom steps S503 to 5505 will be described below.

(5) About Combined BSE Image and Combining Processing (S503)

A combined BSE image and combining processing (step S503 in FIG. 5) willbe described in detail. BSE images are formed by signals obtained fromelectrons backscattered after impinging on the backscattered electrondetectors. The pattern is seen in different ways depending on thepositions at which the backscattered electron detectors are disposedwith respect to the pattern. For example, in a case where the twobackscattered electron detectors 601 and 602 are disposed obliquely inleft and right positions above the upper surface of a pattern element asshown in FIG. 6, backscattered electron images from the backscatteredelectron detectors 601 and 602 are as shown in FIGS. 7A and 7B. FIG. 7Ashows a BSE-L image formed from backscattered electron informationobtained by the backscattered electron detector (L) 601. FIG. 7B shows aBSE-R image formed from backscattered electron information obtained bythe backscattered electron detector (R) 602. The backscattered electrondetector (L) 601 can detect backscattered electrons emitted from a leftside wall and an upper side wall of the pattern element but cannotdetect backscattered electrons emitted from a right side wall and alower side wall under the influence of irregularities of the patternelement. Therefore the backscattered electron detector (L) 601 obtainsan image such as shown in FIG. 7A. In contrast with the backscatteredelectron detector (L) 601, the backscattered electron detector (R) 602can detect backscattered electrons emitted from the right side wall andthe lower side wall of the pattern element. Therefore the backscatteredelectron detector (R) 602 obtains a BSE-R image such as shown in FIG.7B.

An SE image of the pattern element shown in FIG. 6 is as shown in FIG.8A. The SE image is formed by collecting secondary electron signalsemitted from the wafer surface by irradiating the wafer with theelectron beam by utilizing an electric field produced by a voltageapplied to the secondary electron detector. In the SE image, therefore,information on a pattern edge portion and projecting portion can bevisualized without being influenced by irregularities as in the BSEimages. In some case, however, the contrast in a portion of the imagemay be disturbed under the influence of electrification caused byirradiation of the pattern element with the electron beam, as shown inFIG. 8A, resulting in a state such as shown in FIG. 8B, where it isdifficult to extract the contour of the pattern element.

In comparison with an SE image, BSE images are not easily influenced byelectrification. Therefore, BSE images are suitable for extractingpattern contour lines. However, failure to extract a contour line occursat some position under the influence of irregularities of a patternelement in the case of using one BSE image formed by using onebackscattered electron detector as described above. An image effectivein extracting a contour line, such as the one shown in FIG. 7C, can beformed by combining a plurality of BSE images (e.g., the BSE-L imageshown in FIG. 7A and the BSE-R image shown in FIG. 7B) obtained at aplurality of points.

A BSE image is ordinarily a gray-scale image of 8 to 16 bits/pixel.Description will be made of BSE images by assuming that the BSE imagesare gray-scale images of 8 bits/pixel (0 (black) to 255 (white)) forease of description. An ordinary BSE image is formed so that a portionof a high backscattered electron intensity is white, as in the patterncontour portion shown in FIG. 7A or 7B, while the other portions havinglow backscattered electron intensities are black. Also, there is adifference in luminance value between recesses and projections in apattern. There are roughly two kinds of method of extracting patterncontour lines from such BSE images. One of them is a method of detectinga white line portion from a pattern as shown in area A 701 in FIG. 7Aand forming a contour line on the basis of the detected portion (seemethod 1 shown in FIG. 9(1)). The other of them is a method of detectinga portion where the luminance value changes stepwise as shown in area B702 in FIG. 7A, and forming a contour line on the basis of the detectedportion (see method 2 shown in FIG. 9(2)). Since images suited for thedifferent method used for contour line extraction are different fromeach other, different BSE image combining methods are used. For example,when the contour line extraction method of detecting a white line isused, combining processing is performed so as to leave a white line of apattern element from a plurality of BSE images, as in a combined BSEimage shown in FIG. 10A. When the contour line extraction method ofdetecting a portion where the luminance changes stepwise is used,combining processing for leaving a portion where the luminance changesstepwise as in a combined BSE image shown in FIG. 10B is performed.

As combining processing for detecting a white line, combining processingis performed by comparing the luminance values of pixels at positions ona pattern corresponding to each other between a plurality of BSE imagesas shown in FIG. 11 and by selecting the pixels having the highestluminance value as a luminance value in the result of the combining.Another effective combining means is summation, which is processingincluding adding together the luminance values of pixels at positions ona pattern corresponding to each other between a plurality of BSE images,dividing the addition result by the number of pixels having the pixelvalues added together, and obtaining the division result as a luminancevalue in the result of the combining. Summation of a plurality of imagesis an image combining means generally used for the purpose of reducingwhite noise (noise containing all frequency components) superimposed onthe images. Summation may be applied to BSE images to enable forming acombined BSE image having a pattern white portion left therein as wellas reducing white noise superimposed on the BES images. While an exampleof summation in which the luminance values of a plurality of BSE imagesoccupying the pixel value after summation are equally proportioned hasbeen described, a combined BSE image in which differences between theluminance ranges of a plurality of BSE images for example are correctedmay be formed by differently weighting the pixel values of the pluralityof BSE images and thereafter performing summation such as adding thepixel values. As combining processing for detecting a portion where theluminance changes stepwise, combining processing is performed bycomparing the luminance values of pixels at positions on a patterncorresponding to each other between a plurality of BSE images as shownin FIG. 12 and by selecting the pixels having the lowest luminance valueas a luminance value in the result of the combining.

Combined BSE images suitable for contour line extraction can be formedby taking BES images at a plurality of points and combining the BEEimages by computational processing including comparison, addition anddivision. The above-described combining methods are not exclusivelyused. Any other combining method may suffice if a pattern portioncontained in a single image and ineffective in contour line extractionto be applied is removed from BSE images taken at a plurality of points,or if a pattern portion effective in contour line extraction to beapplied is enhanced.

Further, a combined image, such as that shown in FIG. 6, based on BSEimages obtained by a small number of backscattered electron detectorshas certain regions, such as those indicated in circles, where it isdifficult to detect backscattered electrons. That is, the luminancevalue of a pattern in such regions tends to be lower than the luminancevalue of the pattern in other regions. Such a condition badly influencescontour line extraction. Also, noise such as a thermal noise issuperimposed on BSE images to badly influence contour line extraction.Therefore, smoothing and noise removal processing, e.g., those disclosedin the sections describing an improvement in image quality, imagere-forming, smoothing and noise removal in “Computer Image Processing”written by Hideyuki Tamura (Ohmsha, December 2002) are thereforeperformed. By these kinds of processing, portions locally reduced inluminance can be reduced and noise superimposed on a combined BSE imagecan be suppressed, thus enabling a combined BSE image effective incontour line extraction to be formed.

An example of combining images by using two backscattered electronimages obtained by two backscattered electron detectors disposed at 180°intervals about a specimen as shown in FIG. 6 has been described.However, if, for example, three backscattered electron detectors 1201 to1203 are disposed at 120° intervals about a specimen as shown in FIG.13, backscattered electrons emitted in various directions can bedetected with stability. Three backscattered electron images obtainedwith this arrangement may be combined by the above-described method toform a combined BSE image suitable for contour line extraction. Even insuch a case, it is desirable to apply smoothing, noise removalprocessing (“Computer Image Processing”) to the combined BSE imagebecause it is difficult to detect backscattered electrons from someportions.

The number of BSE images to be combined may be increased by disposingfour or more backscattered electron detectors at intervals equal to orsmaller than 120° to form an image suitable for contour line extraction.However, the manufacturing cost of the equipment is increased in such acase. It is desirable to adopt an arrangement according to anexamination purpose and a moderate equipment cost. The number ofbackscattered electron detectors, the number of BSE images to becombined and the positions at which backscattered electron detectors aredisposed are not limited to these in the above-described example.

(6) BSE Image Contour Line Extraction Processing (S504)

Processing for extracting a contour line from BSE images after combiningthe BSE images (step S504 in FIG. 5) will be described in detail. FIG.14 is a flowchart for explaining contour line extraction processing. Forcontour line extraction, the method of detecting a white line in animage and the method of detecting a portion where the luminance changesstepwise in an image exist, as described above. The detection methodsmay be changed only by changing edge enhancement processing in theprocess shown in the flowchart. Steps of this processing will bedescribed.

Referring to FIG. 14, the processing control section 115 first reads acombined B SE image in the image memory 152 (S1401). The processingcontrol section 115 subsequently forms, by edge enhancement processing,an image in which the edge of a pattern element contained in thecombined BSE image is enhanced (hereinafter referred to as “edge image”)(S1402). Use of the edge image facilitates pattern contour lineextraction.

In the case where BSE images are combined so that a white line is formedfrom a pattern portion, an edge image in which a white line is enhancedcan be formed from the combined BSE image, for example, by filteringprocessing using a line detecting operator such as that disclosed in thesection for extraction of an image feature and detection of a line in“Computer Image Processing” (written by Hideyuki Tamura). In the casewhere BSE images are combined so that a portion where the luminancechanges stepwise is formed from a pattern, an edge image in which aportion where the luminance changes stepwise is enhanced can be formedfrom the combined BSE image, for example, by filtering processing usingan edge detecting operator such as that disclosed in the section forextraction of an image feature and detection of an edge on the basis ofa gradient in “Computer Image Processing”. Thus, an image in which anedge of a pattern element is enhanced can be formed by selecting fromdifferent kinds of edge enhancement processing according to the state ofa luminance distribution over the pattern element obtained by combininga plurality of BSE images (a white line or a portion where the luminancechanges stepwise).

Subsequently, the processing control section 115 performs binarizationprocessing (S1403) and thinning processing on an edge image (S1404)disclosed in the section for binary image processing in “Computer ImageProcessing” to form pattern contour data such as shown in FIG. 15. Whenprocessing on all the pixels is performed (S1405), the contour data isstored in the image memory 152 (S1460). A0 to A6 in FIG. 15 representcoordinate information on the contour line position in section A.

While contour data in the description of the present embodimentexpresses a pattern contour line position in an image as coordinateinformation on a pixel-by-pixel basis, sub-pixel position estimationprocessing by a fitting function, e.g., one disclosed in the section fordetection of a pattern element and a figure in “Digital ImageProcessing” complied under the supervision of the Digital ImageProcessing Editing Committee (Computer Graphic Arts Society, March 2006)is performed on edge images. This processing enables forming contourdata expressing a pattern contour line position as coordinateinformation of less than one pixel and determining the pattern contourline position with high accuracy. Further, processing for lineapproximation of a line figure such as that disclosed with respect tobinary image processing in “Computer Image Processing” may be applied tocontour data detected by thinning and sub-pixel position estimation orthe like to reduce the amount of information formed as contour data. Forexample, there is a need to hold all the pixel coordinates (A0 to A6) ofthe contour line position with respect to section A of a contour linesuch as shown in FIG. 15 if the contour line is treated as coordinateinformation on a pixel-by-pixel basis. However, if the contour line isapproximated as a straight line, holding only the pixel coordinates (A0and A6) of the starting and end points of the straight line may suffice.A reduction in the amount of contour line data can be achieved in thisway.

Pattern contour data is generated from a combined BDE image by theabove-described contour line extraction processing. While an example ofcombining a plurality of BSE images has been described as a means forgenerating contour line data from a plurality of BSE images, contourdata may be generated in a different way. For example, a process may beperformed in which the above-described contour line extraction isperformed with respect to a plurality of BSE images and the results ofthe contour line extraction are combined. Contour data is a diagramshowing the existence/nonexistence of a contour at each of coordinateson an image, and can therefore be generated by referring to a pluralityof groups of contour data and selecting, as a combining result, onlyimage portions in which contours exist.

(7) About Pattern Inspection Processing (S505)

Processing for examining a pattern by comparing contour data and designdata (S505) will be described below in detail.

FIG. 16 is a flowchart for explaining pattern inspection processing indetail. The processing control section 115 first reads contour data fromthe image memory 152 (S1601) and a template of design data registered inthe image taking recipe preparation system 125 (S1602).

Next, the processing control section 115 determines an examinationposition by pattern matching (S1603). The reason for determining anexamination position is because an SEM view field misalignment occursdue to an SEM stage accuracy problem for example, as described above.Comparison between a pattern element according to contour data anddesign data without positioning is, for example, as shown in FIG. 17A.In such a case, it is difficult to compare design data 1702 and theshape of a pattern element according to contour data 1701. Therefore,examination based on comparison of the shape of the pattern element isperformed after determining an examination position by pattern patching,as shown in FIG. 17B. A normalized correlation method and a minimalresidual method for example are generally known as a pattern matchingmethod. However, such methods are based on detecting a detectionposition at which the shapes of pattern elements generally conform toeach other, and entail difficulty in performing positioning in a casewhere, as shown in FIGS. 17A and B, design data 1702 and the shape of apattern element according to contour data 1701 differ from each other tosome degree. For this reason, the shape according to the design data isadjusted to the shape of the pattern element on the wafer and anexamination position is thereafter determined by pattern matching basedon normalized correlation, as disclosed in JP Patent Publication (Kokai)No. 6-96214 (1994). As a result, positioning can be performed withaccuracy even in a case where the shape of a pattern element differsfrom that for comparison.

Subsequently, the processing control section 115 compares the designdata and the shape of the pattern element according to the contour data(S1604) and detects as a defect data a portion having a large differencein shape from the design data (S1605). For example, as shown in FIG. 18,comparison of the shape of the pattern element can be realized bymeasuring the distance between design data 1802 and a contour line 1801prepared as straight-line data by the above-described line approximationprocessing. The form of ordinary design data is such that thecoordinates of the starting and end points of a straight lineconstituting a pattern element are defined. Accordingly, the state ofdifference between the design data and the shape of the pattern elementcan be estimated, for example, by measuring the distance 1803 betweeneach of the starting points, the midpoints and the end points ofstraight lines of the contour data and the corresponding straight lineof the design data existing in a direction normal to the straight lineof the contour data, as shown in FIG. 18. A disconnection of the patternelement, such as shown in FIG. B, a short circuit of the patternelement, such as shown in FIG. 18C, or a portion having a largedifference in shape from the design data can be detected by detecting acontour line portion having a distance out of a certain range as adefect.

Data (shape information such as a coordinate position and a length) on adefect in the pattern element detected by comparison between the designdata and the shape of the pattern element according to the contour dataas described above is written to the image memory (S1606).

As shown in FIG. 19, BSE image 1092, a combined BSE image 1903, contourline and design data 1904, defect data 1905 and a measurement points1906 on a wafer may be displayed on a display 1901 of theabove-described electronic computer 116 (see FIG. 1) to provide theexamination results and the progress of examination to a user.

(8) Summary of the First Embodiment

According to the present embodiment, as described above, a contour lineof a pattern element necessary for examination of a semiconductorcircuit based on design data is extracted from an image obtained bycombining a plurality of BSE images taken from two or more points aboutthe pattern element. As a result, the occurrence of erroneous detectionof a contour line position under the influence of a disturbance in animage due to electrification caused when an SE image is used insemiconductor examination can be reduced and design data and a patternelement can be examined with accuracy.

While a pattern on a wafer is examined in the present embodiment, thepresent invention is also effective in examination of a lithography maskpattern made from semiconductor circuit design data. The structure ofmasks presently used in most cases is such that a pattern is formed on aglass member, which is an insulating material, by using chromium, whichis a conductor. The glass is electrified by irradiation with an electronbeam accompanying pattern inspection to badly influence patterninspection. Also, in examination of a resist pattern in the course ofmaking a mask, the resist pattern is electrified. It is apparent thatthe present invention is effective in examining such a mask easilyelectrifiable.

The pattern contour extraction method according to the presentembodiment is also effective in computing a pattern size or a patternspacing size with good reproducibility. In this case, reference tosemiconductor circuit design data is not necessarily required.Processing is performed as shown in the flowchart of FIG. 20. Afterextraction of a contour line, measurement (S2001) and writing (S2002) ofa size value are performed. Thus, use of the contour line extractionmethod according to the present embodiment enables an image having adefinite contour to be obtained even in examination using an insulatingmember easily electrifiable and a large current. If distance measurementis performed by using this image, size measurement can be performed byutilizing electrification robustness which is an advantage of thepresent invention.

<Second Embodiment>

(1) Pattern Inspection Processing

FIG. 21 is a flowchart for explaining pattern inspection processingaccording to a second embodiment of the present invention. Patterninspection method according to the second embodiment is characterized inthat an object from which a contour line to be used for comparison withdesign data is to be extracted can be selected from BSE images and an SEimage.

A BSE image can be said to be an image suitable for contour lineextraction because it is not easily affected by electrification incomparison with an SE image. In some case, however, an SE image can beobtained as an image more advantageous in contour line extraction,depending on SEM observation conditions, and wafer conditions includingthe wafer material and a manufacturing step condition. For example, in acase where pattern inspection is performed by taking BSE images in ahigh-pattern-density area at a low magnification as shown in FIG. 22A,there is a possibility of each of pattern element portions of the BSEimages being formed so as to have, as shown in FIG. 22B, a wider whiteline width (contour line increased in thickness) relative to that in anSE image (FIG. 22D) taken from the same area. When combining processingusing such BSE images is performed to leave the white lines of thepattern element portions, the white lines of the pattern elementsadjacent to each other overlap each other as shown in FIG. 22B so thatthe contour line of in a portion 2201 indicated by the broken line inFIG. 22C cannot be accurately extracted (the contour lines to berecognized as two are extracted as one contour line) and the comparisonof the resulting image with the design data is difficult to make.Electrification, which is a consideration with respect to an SE image,occurs as a result of irradiation of the semiconductor pattern with alarge amount of electron beam, for example, when the SEM current valueis high and/or the observation magnification is high. Therefore, in acase where pattern inspection is performed by taking images at a lowmagnification from an area where the pattern element density is high,the influence of electrification is reduced and a pattern elementcontour line can be accurately extracted even by using an SE image, asshown in FIG. 22E, thus enabling comparison with the design data. Ifeach of BSE images and an SE image contain pattern information effectivein the above-described contour line extraction, combining processingsuch as that described above may be performed between the SE image andthe BSE images to form an image effective in contour line extraction.

Referring to FIG. 21, the processing control section 115 first reads adesign data template corresponding to the coordinates of an EP from theimage taking recipe preparation system 125 (S2101). Subsequently, theprocessing control section 115 determines, according to a command from auser, which one of an SE image, BSE images, and an image obtained bycombining the SE and BSE images is to be used in execution of patterninspection (S2102).

If execution of examination using the SE image is designated, theprocessing control section 115 reads out the SE image from the imagememory 152 (S2103).

If execution of examination using the BSE images is designated, theprocessing control section 115 reads out the BSE images from the imagememory 152 (S2104) and combines the BSE images (S2105).

If execution of examination using a combined image of the SE image andBSE images is designated, the processing control section 115 reads outthe SE and BSE images from the image memory 152 (S2106 and S2107) andcombines the SE and BSE images (S2108).

The processing control section 115 extracts a contour line from thecombined image obtained in step S2103, S2105 or S2108 (S2109) andexamines the pattern by comparing the contour data and the design data(S2110). Data (shape information such as a coordinate position and alength) on a defect in the pattern detected by comparison between thedesign data and the configuration of the pattern according to thecontour data as described above is written to the storage 123 forexample (S2111). To image combining processing (S2105 or S2108) andcontour extraction processing (S2109), the corresponding processingsdescribed in the description of the first embodiment can be applied.

(2) Summary of the Second Embodiment

As described above, pattern inspection using design data can beperformed with stability by changing, according to SEM image takingconditions and wafer conditions, images from one of which a contour lineshould be extracted.

Selection of one of images from which a contour line should be extractedis executed on the basis of a user designation given through theelectronic computer 116 connected to the processing control section 115according to the description with reference to the flowchart of FIG. 21.A different process is conceivable in which images to be processed,advantageous in contour line extraction according to image takingconditions and wafer conditions, are empirically obtained and held astable information in the processing control section 115 as shown in FIG.23, and a selection of one of the images from which a contour lineshould be extracted is made according to information including imagetaking conditions and wafer conditions from the SEM and the image takingrecipe generation section. When an image taking recipe is prepared inthe image taking recipe preparation section 125, parameters enabling theprocessing control section 115 to select one of the images from which acontour line should be extracted may be registered in the image takingrecipe.

According to the present embodiment, as described above, one of an SEimage and BSE images can be selected as an image from which a contourline in a pattern should be extracted to be used in semiconductorcircuit examination based on design data; a contour line is extractedfrom the selected image; and examination by comparison with the designdata is performed, thus enabling selection of an image effective incontour line extraction, which is changed depending on SEM image takingconditions and wafer conditions, and enabling examination using acorrect pattern contour line.

<Other Embodiments>

The present invention can also be implemented by means of a program codeof software capable of realizing the functions of the embodiment. In thecase of using such a program code, a storage medium on which the programcode is recorded is provided to a system or a unit, and a computer (or aCPU or an MPU) in the system or the unit reads out the program codestored in the storage medium. In this case, the program code itself,read out from the storage medium, realizes the functions of theabove-described embodiment, and the program code itself and the storagemedium on which the program code is stored constitute the presentinvention. As the storage medium for supplying such a program code, afloppy (registered trademark) disk, a CD-ROM, a DVD-ROM, a hard disk, anoptical disk, a magneto-optical disk, a CD-R, a magnetic tape, anonvolatile memory card or a ROM for example is used.

Also, an operating system (OS) running on the computer may perform partor the whole of the actual processing on the basis of instructions fromthe program code, and the functions of the above-described embodimentmay be realized by the processing. Further, after the program code readout from the storage medium has been written to a memory on thecomputer, the CPU or the like of the computer may perform part or thewhole of the actual processing to realize the functions of theabove-described embodiment by the processing.

Also, the program code of the software capable of realizing thefunctions of the embodiment may be distributed via a network. Theprogram code is thereby stored in a storage means such as a hard disk ora memory in the system or unit, or on a storage medium such as a CD-RWor a CD-R. The computer (or a CPU or an MPU) in the system or unit mayread out the program code stored in the storage means or on the storagemedium and execute the program code to achieve the functions of theembodiment.

1. An apparatus for processing an image of a sample having a patternthat is obtained by scanning electron microscope, said apparatuscomprising: a memory for storing a backscattered electron image obtainedby the scanning electron microscope; a processor for extracting contourdata of the pattern from the backscattered electron image; wherein saidmemory stores a secondary electron image of the sample in addition tothe backscattered electron image; and said processor executes processingfor combining the backscattered electron image and the secondaryelectron image, and extracts the contour data based on the combinedimage.
 2. The apparatus according to claim 1, wherein: said memorystores a plurality backscattered electron images from a plurality ofviewing points in the scanning electron microscope; and said processorexecutes combining processing of the plurality of the backscatteredelectron images, and extracts the contour based on the combined image.3. The apparatus according to claim 1, wherein: said memory stores aplurality backscattered electron images from a plurality of viewingpoints in the scanning electron microscope; and said processor executescombining processing of the plurality of the backscattered electronimages, and extracts the contour based on the combined image; saidapparatus further comprises a display for displaying a graphical userinterface for a user to command which type of image is to be used forcombining processing; and the processor executes the combiningprocessing based on the command.
 4. An apparatus for processing an imageof a sample having a pattern, which is obtained by scanning electronmicroscope, said apparatus comprising: a storage that stores programcode for extracting contour data of a pattern from a backscatteredelectron image obtained by the scanning electron microscope; a processorfor executing the program; and wherein said storage stores program codefor combining processing of the backscattered electron image and asecondary electron image, and program code for extracting contour datafrom the combined image of the backscattered electron image and thesecondary electron image.
 5. The apparatus according to claim 4, whereinsaid storage stores program code for combining processing of pluralbackscattered electron images obtained from a plurality of viewingpoints in the scanning electron microscope, and program code forextracting contour data from the combined image of the pluralbackscattered electron images.
 6. The apparatus according to claim 4,wherein: said storage stores program code for combining processing ofplural backscattered electron images obtained from a plurality ofviewing points in the scanning electron microscope, and program code forextracting contour data from the combined image of the pluralbackscattered electron images; said apparatus further comprises adisplay for displaying a graphical user interface for user to commandwhich type of image is to be used for the combining processing; and theprocessor executes the combining processing based on the command.